Technical Field
The present invention relates to a bag mouth opening method and apparatus for use in bag filling and packaging in which a bag is held in a suspended position by being gripped at its laterally opposite side edges with a pair of grippers (left and right grippers) movable toward and away from each other, and the bag held in this way is moved along a predetermined path to open the bag mouth, fill an article to be packaged into the bag from the opened bag mouth, and seal the bag mouth in the course of the movement. More particularly, the present invention relates to a method of and apparatus for opening a mouth portion of a bag having a spout attached to an upper edge-side portion thereof, which is called a spout bag.
Background Art
Spout bags may be used in packaging of liquid material, for example. A bag filling and packaging machine disclosed in Japanese Patent No. 3,261,543 shows one example of packaging using spout bags. The bag filling and packaging machine successively carries out the following packaging processes: feeding the packaging machine with a bag having no spout attached thereto (first step); attaching a spout to the bag (third and fourth steps); opening the bag mouth (fifth step); filling an article to be packaged into the bag (sixth step); sealing the bag mouth (seventh and eighth steps); and so forth. There is also known a bag filling and packaging process in which a bag having a spout attached thereto previously is fed to a bag filling and packaging machine, in which are successively carried out opening the bag mouth, filling an article to be packaged, sealing the bag mouth, etc.
In bag filling and packaging, the bag mouth needs to be opened surely and stably for the following reasons. If the bag mouth cannot be opened in a desired shape or the opened bag mouth cannot be stably kept in the desired shape, the process of filling an article to be packaged may be hindered, for example, by an error in insertion of a liquid material-filling nozzle into the bag. There are bags having a spout attached to an upper edge-side portion thereof, e.g. a corner spout bag having a spout attached to an upper end corner thereof as shown in FIG. 5a of Japanese Patent No. 3,261,543, and a bag having a spout attached thereto at a position predetermined distance rightward or leftward from the upper end center of the bag as shown in FIG. 5b of the same Japanese Patent No. 3,261,543.Such spout bags are provided with an opening for filling an article to be packaged at a position different from but relatively close to the position where the spout is attached. Therefore, there may be a hindrance to the operation of opening the bag mouth with an opening device generally using suction cups
More specifically, a bag is flat on the whole before being opened at the mouth thereof. Therefore, a spout bag having a spout attached to the top thereof, particularly a corner spout bag, involves the following problem. As shown in FIGS. 1A, 1B and 1C, which are a front view, a plan view, and a side view, respectively, the spout S undesirably tilts by gravity above the grippers G gripping the bag B, causing the bag body Bb to bend at the periphery of the position where the spout S is attached (i.e. at the periphery of the bag mouth). In such a case, there may be an error in the operation of opening the bag mouth using the suction cups C. Even if the bag mouth can be opened, the opened bag mouth may fail to stably keep a desired shape, which may give rise to a problem in the process of filling an article to be packaged, which is carried out afterward. This problem remarkably occurs in the case of a bag that is thin in thickness of the film constituting the bag body and hence that is not very stiff.